Most people know that losing weight boils down to eating fewer calories and/or exercising more. That's what nutritionists tell us, wagging their fingers, every time we fall en masse for the latest fad diet. A calorie is a calorie, they said, when Americans jumped on the Atkins bandwagon, gorging themselves on steak, eggs and blue cheese dressing.

The only problem is that calories really aren't all the same. Sure, they may provide the same amount of energy, but different foods affect the body in different ways—from the cell-protecting properties of antioxidants to the feel-good consequences of chocolate.

University of Washington researchers have found that protein has a strong effect on appetite, perhaps one key reason why so many dieters have successfully dropped pounds on high protein diets (at least in the short term). The surprising part is that how many carbohydrate calories are in your diet has nothing to do with the weight loss. The study found that simply increasing the amount of protein in your diets can help you lose weight even if you don't cut back on carbohydrates at all.

For most Americans, protein makes up 15 percent of their daily caloric intake, while 35 percent comes from fat and 50 percent from carbohydrates. In the study, researchers had subjects bump up their protein intake to 30 percent. Fat was reduced to 20 percent.

Within three months the subjects had lost an average of 11 pounds, even though half of the calories they ate still came from carbohydrates. People on the modified diet reported feeling satisfied with less food. In other words, they lost weight because they consumed fewer calories, not because they ate fewer carbohydrates.

Researchers are still trying to figure out exactly how protein has more control over hunger than other nutrients. One possibility is that it makes the central nervous system more sensitive to leptin, a hormone that tells your body when it has stored enough fat.

What researchers do know, however, is that even slightly increasing the amount of protein you eat can help you lose weight without having to banish carbohydrates from your diet. Pumping up protein intake by just 5 to 10 percent could make a difference, says Colleen Matthys, a bionutritionist and one of the study's researchers.

Previous research has shown that protein also helps keep the brain alert. Ever notice that a high carbohydrate lunch can leave you dragging through the afternoon? Carbohydrates can make you feel tired—and hungry for an energy boost—because they increase the brain's level of the amino acid tryptophan, which in turns spurs the brain to make the calming neurotransmitter serotonin. Protein, on the other hand, prompts the brain to manufacture norepinephrine and dopamine, chemical messengers that promote alertness and activity.

Protein is also an essential component of every cell in the body, and we need it to repair and replenish our skin, bones and muscle tissue, as well as for enzymes, hormones and other chemicals. But carbs are equally important, despite their bad rep. Carbs are the brain's main fuel.

Protein's natural power of appetite suppression should be implemented cautiously, says Matthys. She suggests you eat low-fat dairy products, beans, fish and lean cuts of meat, such as skinless chicken and turkey breasts. Even carb-heavy treats, like muffins and cookies, can be made more protein-rich when baked with non-fat powdered milk and egg whites.